1. Field of the Invention
The present application relates to a monitoring method of an apparatus, and more particularly, to a monitoring method of an exposure apparatus.
2. Description of Related Art
A photolithography process is deemed as one of the most important processes in fabrication of semiconductors. Basic parameters affecting critical dimension (CD) in the photolithography process mainly include an exposure dose and a focus. Generally, during an exposure process performed on an exposure apparatus, there is a difference between a real exposure dose and a predetermined exposure dose and between a real focus and a predetermined focus, which are the so-called dose drift and focus drift, respectively. Thereby, the CD of patterns and profiles thereof are influenced. Hence, the exposure dose is frequently compensated according to the final measured CD after the exposure process is performed, and a predetermined exposure dose is provided by an exposure dose set-up system of the exposure apparatus, such that the CD of wafers in the next lot can be closer to a target value. Nonetheless, in the conventional compensation method, it is not likely to deduce the real exposure focus from the final measured CD, and therefore it is impossible to compensate the focus drift.
In light of the foregoing, error tolerance of device dimension is decreased along with the decrease in the device dimension. As such, at this current stage, manufacturers endeavor to accurately monitor and control the exposure dose and the exposure focus of the exposure apparatus for fabricating devices having acceptable critical dimension.